JP4459669B2 - Hydrodynamic bearing device - Google Patents

Abstract

A smooth surface of a shaft member is divided from an outer circumferential surface by a step so that its axial length dimension becomes shorter than the axial length dimension of a hydrodynamic groove region formed on the inner circumferential surface of a bearing sleeve, whereby the hydrodynamic groove regions excluding lower portions of a land between hydrodynamic grooves oppose the smooth surface.

Description

  The present invention relates to a hydrodynamic bearing device that supports a shaft member in a non-contact manner by a hydrodynamic action of a fluid generated between bearing gaps. This bearing device is a spindle motor such as an information device, for example, a magnetic disk device such as an HDD, an optical disk device such as a CD-ROM, CD-R / RW, DVD-ROM / RAM, or a magneto-optical disk device such as MD or MO, It is suitable for polygon scanner motors of laser beam printers (LBP) and other small motors.

  In addition to high rotational accuracy, the various motors are required to have high speed, low cost, low noise, and the like. One of the components that determine the required performance is a bearing that supports the spindle of the motor. In recent years, the use of a hydrodynamic bearing having characteristics excellent in the required performance has been studied or actually used. Yes. For example, in a spindle motor of a disk drive device such as an HDD, a hydrodynamic bearing device that uses a hydrodynamic bearing for each of a radial bearing portion that supports a shaft member in a radial direction and a thrust bearing portion that supports a shaft member in a thrust direction. Used. In this dynamic pressure bearing device, dynamic pressure grooves as dynamic pressure generating means are provided on the inner peripheral surface of the bearing sleeve forming the radial bearing portion or the outer peripheral surface of the shaft member, and the shaft member forming the thrust bearing portion is provided. Dynamic pressure grooves are provided on both end surfaces of the flange portion or on the opposite surfaces (end surface of the bearing sleeve, end surface of the thrust plate, etc.).

When these dynamic pressure grooves are formed, particularly when the dynamic pressure grooves are formed on the inner periphery of the bearing sleeve, the method of processing the dynamic pressure grooves becomes a problem. As an example of this processing method, after inserting a forming die having a groove shape corresponding to the shape of the dynamic pressure groove into the inner periphery of the bearing sleeve material, the bearing sleeve material is compressed in the radial direction with its axial direction restricted. Thus, a method has been proposed in which the inner peripheral surface is pressed against a mold and plastically deformed (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 11-190344

  However, when the dynamic pressure grooves are molded in this way, the compression force acting on the material is close to the non-contact portion with the groove mold in the region where the plurality of dynamic pressure grooves are arranged (dynamic pressure groove region). It is easy to escape, so that it becomes difficult for the meat of the material to be filled in the groove-shaped recess. Therefore, for example, in the dynamic pressure groove region of the radial bearing portion, as shown in FIG. 6B, a so-called “sag” in which the generatrix shape of the back portion 18c between the dynamic pressure grooves 18b becomes lower at both ends in the axial direction. Arise. In this case, as shown in FIG. 7, the gap width G1 at both axial ends of the radial bearing gap is larger than the gap width G2 at the axial center. Therefore, if the bearing design is performed on the assumption that the clearance width between the radial bearing gaps is constant over the entire length in the axial direction, the desired dynamic pressure effect can be obtained because the dynamic pressure effect is reduced in the portion where the clearance width is large. Therefore, the bearing rigidity of the entire bearing is reduced.

  Such a decrease in bearing rigidity can be recovered by, for example, setting the axial length of the dynamic pressure groove regions 18a, 18a to be long, but simply increasing the axial length of the dynamic pressure groove regions 18a, 18a. Since the axial length of the narrow radial bearing gap increases and the fluid resistance in the bearing gap increases, the rotational torque increases.

  Similar problems can occur not only in the radial bearing portion but also in the dynamic pressure groove of the thrust bearing portion. The dynamic pressure groove of the thrust bearing portion is, for example, press-molded using a groove mold corresponding to the shape of the dynamic pressure groove. In that case, the plastic flow occurs in a portion close to the non-contact area with the groove mold as described above. Becomes insufficient, sagging occurs in the generatrix shape of the dynamic pressure groove region, and the same problem as described above occurs.

  Therefore, an object of the present invention is to provide a hydrodynamic bearing device that can prevent a decrease in bearing rigidity based on a sagging of the busbar shape in the hydrodynamic groove region while avoiding an increase in rotational torque.

In order to solve the above problems, a hydrodynamic bearing device according to the present invention includes a hydrodynamic groove region in which a plurality of hydrodynamic grooves are arranged, a smooth surface facing the hydrodynamic groove region, a hydrodynamic groove region, and a smooth surface. In the hydrodynamic bearing device having a bearing clearance formed between the stationary side and the bearing side that generates fluid dynamic pressure by relative rotation between the stationary side and the rotating side, the hydrodynamic groove region is plastically processed by pressing a die corresponding to the shape thereof The smooth surface is partitioned and formed with a step so that the length thereof is shorter than the length of the dynamic pressure groove region , whereby the smooth surface is formed at the sagging portions at both ends of the dynamic pressure groove region. It is characterized by facing the dynamic pressure groove region except for . The “length” here means the axial direction of the smooth surface or dynamic pressure groove region when the normal direction of the smooth surface or dynamic pressure groove region matches the radial direction of the bearing (radial bearing portion). When the normal direction coincides with the thrust direction of the bearing (thrust bearing portion), it means the length in the radial direction of the smooth surface and the dynamic pressure groove region.

  According to this configuration, since the length of the smooth surface is shorter than the length of the dynamic pressure groove region, the smooth surface is substantially constant except for the end portion of the dynamic pressure groove region where the sagging is noticeable. It can be made to oppose the center part of the dynamic-pressure-groove area | region which has thickness. Therefore, it is possible to make the radial bearing clearance almost constant, and to design the length of the entire dynamic pressure groove area so that the specified dynamic pressure effect can be obtained with this constant width bearing clearance, avoiding a decrease in bearing rigidity. Can do. In this case, the length of the entire dynamic pressure groove region is increased as compared with the conventional case, but the smooth surface is partitioned and formed with a step, so that the sagging portion formed at the end of the dynamic pressure groove region is a portion other than the smooth surface. And the gap width of this portion can be made larger than the bearing gap having the constant width. Therefore, an increase in torque due to fluid resistance can be minimized.

  In addition, there is an invention described in Japanese Patent Application Laid-Open No. 2002-70842 as focusing on the magnitude relationship between the smooth surface and the axial length of the dynamic pressure groove region. In this invention, the length of the smooth surface is adjusted. The length is longer than the length of the pressure groove region, and the size relationship is opposite to that of the present application.

  The present invention can be applied to a radial bearing portion constituted by a dynamic pressure bearing. A dynamic pressure bearing device having a radial bearing portion includes a bearing sleeve and a shaft member in addition to the above-described dynamic pressure groove region, smooth surface, and bearing gap. The radial bearing gap as the bearing gap is formed between the inner peripheral surface of the bearing sleeve and the outer peripheral surface of the shaft member, and the shaft member is supported in a non-contact manner in the radial direction by the fluid dynamic pressure formed in the radial bearing gap. Is done. In this case, for example, the dynamic pressure groove region can be formed on the inner periphery of the bearing sleeve, and the smooth surface can be formed on the outer periphery of the shaft member.

  The present invention can also be applied to a hydrodynamic bearing device having a thrust bearing portion constituted by a hydrodynamic bearing. In this hydrodynamic bearing device, a shaft member is provided with a flange portion projecting to the outer diameter side, and the bearing clearance is between the end surface of the flange portion and the surface facing the end surface in addition to the radial bearing clearance. Is also formed (thrust bearing gap). The shaft member is supported in a non-contact manner in the thrust direction by the fluid dynamic pressure formed in the thrust bearing gap. In this case, the dynamic pressure groove region is formed on either one of the end surface of the flange portion of the shaft member or the surface facing this, and the smooth surface is formed on the other.

  The dynamic pressure groove region is preferably formed into a predetermined shape (herringbone shape, spiral shape, etc.) by pressing a mold corresponding to the shape and plastic working. Since the mold is pressed, dynamic pressure groove forming by rolling is excluded, and plastic working is excluded, and dynamic pressure groove forming by, for example, resin injection molding without plastic deformation of the material is also excluded.

  By configuring the motor with the above-described hydrodynamic bearing device, it is possible to provide a motor with high rotational accuracy and low torque.

  As described above, according to the hydrodynamic bearing device according to the present invention, it is possible to prevent a decrease in bearing rigidity due to the busbar shape sagging in the hydrodynamic groove region while avoiding an increase in rotational torque.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 conceptually shows the overall configuration of a spindle motor for information equipment incorporating a fluid dynamic bearing device according to an embodiment of the present invention. This spindle motor for information equipment is used in a disk drive device such as an HDD, and includes a hydrodynamic bearing device 1 that supports the shaft member 2 in a non-contact manner in a freely rotatable manner, a disk hub 3 mounted on the shaft member 2, A motor stator 4 and a motor rotor 5 are provided to face each other via a radial gap. The motor stator 4 is attached to the outer periphery of the casing 6, and the motor rotor 5 is attached to the inner periphery of the disc hub 3. The housing 7 of the hydrodynamic bearing device 1 is mounted on the inner periphery of the casing 6. The disk hub 3 holds one or more disks D such as a magnetic disk. When the motor stator 4 is energized, the motor rotor 5 is rotated by the exciting force between the motor stator 4 and the motor rotor 5, whereby the disk hub 3 and the shaft member 2 are rotated together.

  FIG. 2 shows the hydrodynamic bearing device 1. The hydrodynamic bearing device 1 includes a bottomed cylindrical housing 7 having an opening 7a at one end and a thrust plate 7c at the other end, a cylindrical bearing sleeve 8 fixed to the inner periphery of the housing 7, and a bearing sleeve. The shaft member 2 to be inserted into the inner periphery of 8 and the seal member 9 fixed to the opening 7a of the housing 7 are configured as main members. For convenience of explanation, the following description will be made with the opening 7a side of the housing 7 as the upward direction and the thrust plate 7c side of the housing 7 as the downward direction.

  The housing 7 is formed of, for example, a soft metal material such as brass, and includes a cylindrical side portion 7b and a disc-covered thrust plate 7c serving as a bottom portion of the housing 7 as separate structures. On the inner bottom surface of the thrust plate 7c, a dynamic pressure groove region 7c1 such as a spiral shape in which a plurality of dynamic pressure grooves 7c2 (see FIG. 5) are arranged is formed by press working. Further, a large diameter portion 7e having a larger diameter than other portions is formed at the lower end of the inner peripheral surface 7d of the side portion 7b of the housing 7, and a thrust plate 7c is caulked, adhered, etc. to the large diameter portion 7e. It is fixed by means of

  The bearing sleeve 8 is formed in a cylindrical shape with a porous body made of sintered metal, for example, a sintered metal porous body mainly containing copper. On the inner periphery of the bearing sleeve 8, for example, as shown in FIG. 3A, herringbone-shaped dynamic pressure groove regions 8 a and 8 a in which a plurality of dynamic pressure grooves 8 b and 8 b are arranged are separated in the axial direction. Two places are formed. On the lower end surface 8e of the bearing sleeve 8, a dynamic pressure groove region 8e1 having a spiral shape or the like in which a plurality of dynamic pressure grooves 8e2 (see FIG. 5) are arranged is formed.

  Both the dynamic pressure groove region 8a on the inner periphery of the bearing sleeve and the dynamic pressure groove region 8e1 on the lower end surface 8e are molded. Among these, the dynamic pressure groove region 8a formed on the inner peripheral surface of the bearing sleeve 8 is inserted into the inner periphery of the bearing sleeve material after inserting a core rod having a groove shape corresponding to the dynamic pressure groove shape of each region 8a. The sleeve material is pressed in the radial direction with its axial direction constrained, the inner peripheral surface is pressed against the core rod, and the groove shape is transferred by plastic deformation of the inner peripheral surface. The mold removal of the core rod after the plastic working can be smoothly performed without causing interference with each other by the spring back of the bearing sleeve material accompanying the release of the compression force. The dynamic pressure groove region 8e1 formed on the lower end surface 8e of the bearing sleeve 8 forms a groove shape corresponding to the shape of the dynamic pressure groove on the end surface of a jig (punch or the like) that restrains the bearing sleeve material from the axial direction. By this, it can shape | mold simultaneously with the dynamic pressure groove area | region 8a of an internal peripheral surface.

  The shaft member 2 is made of a metal material such as stainless steel, for example, and includes a shaft portion 2c and a flange portion 2b provided integrally or separately at the lower end of the shaft portion 2c. As shown in an enlarged view in FIG. 4, the shaft portion 2c has a stepped shaft shape, and is a region of the outer peripheral surface 2a of the shaft portion 2c that faces two dynamic pressure groove regions 8a on the inner periphery of the bearing sleeve after the assembly of the bearing. Are formed with a cylindrical smooth surface 2d having a diameter larger than that of other portions and having no irregularities. Both sides of the smooth surfaces 2d and 2d in the axial direction are partitioned by a step H from the outer peripheral surface 2a excluding the smooth surfaces 2d and 2d. The length dimension B in the axial direction of both smooth surfaces 2d is smaller than the length dimension A in the axial direction of the corresponding dynamic pressure groove region 8a (see FIG. 3), and both smooth surfaces 2d are all in their entire regions. Is opposed to the dynamic pressure groove region 8a.

  In FIG. 4, the size of the step H is exaggerated for easy understanding, but in practice, the step H is suitably 10 μm or more. If the level difference H is smaller than 10 μm, it is considered that the torque reduction effect described later becomes insufficient. The depth of the dynamic pressure groove is actually about 1 to 20 μm, but this is exaggerated in the drawing.

  The seal member 9 has an annular shape, and is fixed to the inner peripheral surface of the opening 7a of the housing 7 by means such as press-fitting and bonding as shown in FIG. In this embodiment, the inner peripheral surface of the seal member 9 is formed in a cylindrical shape, and the lower end surface 9 a of the seal member 9 is in contact with the upper end surface 8 f of the bearing sleeve 8.

  After the assembly of the hydrodynamic bearing device 1, the shaft portion 2 c of the shaft member 2 is inserted into the inner periphery of the bearing sleeve 8, and the flange portion 2 b is the lower end surface 8 e of the bearing sleeve 8 and the inner bottom surface of the thrust plate 7 c of the housing 7. It is accommodated in the space part between. At this time, between the tapered outer peripheral surface of the shaft portion 2 c facing the inner peripheral surface of the seal member 9, a taper-shaped seal space that gradually expands toward the outside direction of the housing 7 (upward in the figure). S is formed. The internal space of the housing 7 sealed with the seal member 9 is filled with lubricating oil including the internal holes of the bearing sleeve 8, and the oil level of the lubricating oil is maintained in the sealing space S.

  When the shaft member 2 is rotated with respect to the bearing sleeve 8 in this state, the dynamic pressure of the lubricating oil is generated between the radial bearing gaps between the smooth surface 2d of the shaft member 2 and the dynamic pressure groove region 8a opposed thereto. The first radial bearing portion R1 and the second radial bearing portion R2 that support the shaft member 2 in the radial direction in a non-contact manner are formed apart from each other in the axial direction. At the same time, each thrust bearing gap between the lower end surface 8e of the bearing sleeve 8 and the upper end surface 2b1 of the flange portion 2b of the shaft member 2 and between the inner bottom surface of the thrust plate 7c and the lower end surface 2b2 of the flange portion 2b. The first and second thrust bearing portions S1 and S2 are generated in each of which the dynamic pressure of the lubricating oil is generated to support the shaft member 2 in the thrust direction in a non-contact manner.

  In the dynamic pressure groove region 8a of the radial bearing portions R1 and R2, this is formed by molding, and as shown in FIG. 3 and FIG. 4, in the shape of the axial line, between the dynamic pressure grooves 8b at both ends in the axial direction. In the present invention, the axial length dimension B of the smooth surface 2d is shorter than the axial length dimension A of the dynamic pressure groove region 8a. The sagging portions at both ends of the dynamic pressure groove region 8a can be eliminated from the facing region, and the smooth surface 2d can be made to face the central portion of the dynamic pressure groove region 8a having a substantially constant groove depth. Therefore, the radial bearing clearance can be made substantially constant, and the axial length of the dynamic pressure groove region 8a is set so that the prescribed dynamic pressure effect can be obtained in the bearing clearance of this constant width, thereby avoiding a decrease in bearing rigidity. can do. This means that the axial length of the dynamic pressure groove region is increased as compared with the conventional bearing design, but even in this case, the sagging portion that is less involved in the dynamic pressure effect is excluded from the region facing the smooth surface 2d. Then, the shaft portion outer peripheral surface 2a having a diameter smaller than that of the smooth surface 2d is opposed to each other, and the gap width of this portion is made larger than the bearing clearance having a constant width by the step H, so that an increase in torque due to fluid resistance is minimized. Can be suppressed. Accordingly, it is possible to achieve both the contradictory purposes of improving the bearing rigidity and reducing the torque.

  The difference in the axial length between the dynamic pressure groove region 8a and the smooth surface 2d is determined according to the length of the sag portion generated in the dynamic pressure groove region 8a. At present, sagging has occurred in a range of approximately 0.2 mm from both axial ends of the dynamic pressure groove region 8a, and thus the difference in axial length is set to at least twice 0.2 mm, that is, 0.4 mm or more. It is desirable to do.

  In the above description, the dynamic pressure groove regions 8a of the radial bearing portions R1 and R2 are illustrated, but the same configuration can be applied to the dynamic pressure groove regions 8e1 and 7c1 of the thrust bearing portions S1 and S2. These dynamic pressure groove regions 8e1 and 7c1 are also formed by plastically deforming the material by pressing the groove mold corresponding to the dynamic pressure groove shape as described above. Therefore, as schematically shown in FIG. Draft occurs at both ends in the radial direction of the pressure groove regions 8e1 and 7c1, but the smooth surfaces 2b3 and 2b4 are partitioned and formed with steps on both end surfaces 2b1 and 2b2 of the flange portion facing the dynamic pressure groove regions 8e1 and 7c1. By making the length of the smooth surfaces 2b3 and 2b4 in the radial direction shorter than the length of the dynamic pressure groove regions 8e1 and 7c1 facing each other, both improvement in bearing rigidity and reduction in torque in the thrust bearing portions S1 and S2 are achieved. It becomes possible to do. In FIG. 5, the groove depths of the dynamic pressure grooves 8e2 and 7c2 are exaggerated as in FIG.

  In this embodiment, the dynamic pressure groove region 8e1 is formed on the lower end surface 8e of the bearing sleeve 8 and the first smooth surface 2b3 is formed on the upper end surface 2b1 of the flange portion 2b of the shaft member 2. On the contrary, it is also possible to form a smooth surface on the lower end surface 8e of the bearing sleeve 8 and a dynamic pressure groove region on the upper end surface 2b1 of the flange portion 2b. Similarly, the dynamic pressure groove region 7c1 formed on the inner bottom surface of the thrust plate 7c of the housing 7 and the second smooth surface 2b4 formed on the lower end surface 2b2 of the flange portion 2b of the shaft member 2 face each other. And can be formed.

1 is a cross-sectional view of a spindle motor for information equipment incorporating a fluid dynamic bearing device according to an embodiment of the present invention. It is sectional drawing of the fluid dynamic bearing apparatus which concerns on one Embodiment of this invention. (A) is sectional drawing of a bearing sleeve, (b) is a figure which expands and shows the bus-bar shape of the axial direction of the dynamic pressure groove area | region of a bearing sleeve inner periphery. It is a schematic diagram which shows the positional relationship in the radial direction of the dynamic pressure groove area | region which forms a radial bearing clearance, and a smooth surface. It is a schematic diagram which shows the positional relationship in the axial direction of the dynamic pressure groove area | region which forms a thrust bearing clearance, and a smooth surface. (A) is sectional drawing of the conventional bearing sleeve, (b) is a figure which expands and shows the bus-bar shape of the axial direction of the dynamic pressure groove area | region of the inner periphery. It is a schematic diagram which shows the conventional positional relationship in the radial direction of the dynamic pressure groove area | region which forms a radial bearing clearance, and a smooth surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Dynamic pressure bearing apparatus 2 Shaft member 2a Outer peripheral surface 2b Flange part 2b3 Smooth surface 2b4 Smooth surface 2c Shaft part 2d Smooth surface 3 Disc hub 4 Motor stator 5 Motor rotor 6 Casing 7 Housing 7c Bottom part 7c1 Dynamic pressure groove area 7c2 Dynamic pressure groove 7d Inner peripheral surface 7e Large diameter portion 8 Bearing sleeve 8a Dynamic pressure groove region 8b Dynamic pressure groove 8c Back 8e Lower end surface 8e1 Dynamic pressure groove region 8e2 Dynamic pressure groove 9 Seal member A Axial length dimension (dynamic pressure groove region)
B Axial length (smooth surface)
R1 Radial bearing part R2 Radial bearing part S1 Thrust bearing part S2 Thrust bearing part

Claims (4)

It is formed between a dynamic pressure groove region in which a plurality of dynamic pressure grooves are arranged, a smooth surface facing the dynamic pressure groove region, and the dynamic pressure groove region and the smooth surface. In a hydrodynamic bearing device comprising a bearing gap for generating pressure,
The dynamic pressure groove region is plastically processed by pressing a die corresponding to the shape,
The smooth surface is divided and formed with a step so that the length thereof is shorter than the length of the dynamic pressure groove region , and the smooth surface is thus formed by removing the sag at both ends of the dynamic pressure groove region. A hydrodynamic bearing device characterized by facing the groove region . The hydrodynamic bearing device according to claim 1, further comprising a bearing sleeve and a shaft member, wherein the bearing gap is formed between an inner peripheral surface of the bearing sleeve and an outer peripheral surface of the shaft member. The hydrodynamic bearing device according to claim 2, wherein a flange portion projecting toward the outer diameter side is provided on the shaft member, and the bearing gap is further formed between an end surface of the flange portion and a surface facing the end surface. Motor having a dynamic pressure bearing apparatus according to any one of claims 1-3.